Cities whose boundaries were defined centuries ago no longer match the populations they serve with culture, sports events and jobs, says Benjamin R. Barber, the keynote speaker brought to Providence this week by GrowSmartRI and the Providence Preservation Society.

Many visitors who live outside a city’s limits “are free riders on the services, and you can’t tax them,” Barber told The Providence Journal in an interview.

“We need to redefine our cities and city limits and tax structure around the cities, around the areas of the people they actually serve,” he says. “Redistricting is not on the agenda, and it should be.”

Italy’s working on it, Barber says. New Prime Minister Matteo Renzi, former Florence mayor, has proposed a constitutional amendment to reconfigure the country around metro regions.

In the United States, Barber points to Detroit as an example for why redistricting is necessary.

In 1950, Detroit was the fourth largest American city, with 2 million residents and the thriving American auto industry. Its population has dropped to 700,000, all but one or two of its auto manufacturers have left the city, and many schools have closed.

But Barber points this out: the 10 surrounding counties in the Detroit metro region have grown from 3 million to 5 million people, from 1950 until today. Much of the auto industry moved only to surrounding counties, not down south or abroad.

“And those 10 counties today are the fourth most successful new technology, knowledge economy counties in America,” Barber says, alongside Silicon Valley and New York. “Now if Detroit were defined today with those 10 [counties], despite the problems in downtown, it would be one of the most successful cities in America.”

Detroit is attracting entrepreneurs and innovators compelled to take into their own hands what the government isn’t getting done. In contrast, Barber says, Providence is at a disadvantage because it’s a “little too well off.” Thus, it’s not as attractive to take desperate measures here because the city’s “successes get in the way of dealing with its failures.”